Clean up the pipe closing in openvpn_popen()

Clean up the pipe closing in openvpn_popen()

Do the proper closing of the pipe ends which is not being used,
also in error situations.  Moved the closing of the parent side
before the waitpid(), to be consistent with the child side (as
early as possible).

Also improved the error messages with more details.

[v2 - Don't call close() if execve() fails]

Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: 20140909202408.GK1118@greenie.muc.de
URL: http://article.gmane.org/gmane.network.openvpn.devel/9036